I’m allowed 30 days in Singapore visa-free but I’m thinking I might want to stay longer depending on how the trip goes. Is it possible to extend once I’m already there, or do I need to leave and re-enter?
Yes, it is possible to extend your stay in Singapore, though it’s not guaranteed and is at the discretion of the Immigration and Checkpoints Authority (ICA). If you want to stay longer once you’re there, you can apply for an extension at an ICA office in person before your permitted stay expires. Extensions are typically granted for 30 days at a time. The other option some travellers use is a short trip out to a neighbouring country like Malaysia or Indonesia and re-entering, though technically Singapore doesn’t guarantee you’ll be admitted again immediately after leaving.
For the most accurate info on extensions: https://www.ica.gov.sg/enter-transit-depart/extend-your-stay